The present invention relates to a system for controlling the ignition timing of an automotive engine.
The ignition timing must be exactly adjusted, for example at the regular inspection. Generally, the adjustment is performed in idling state by using a timing light under the condition that the ignition timing is fixed to a predetermined value by turning on an ignition timing fixing switch.
However, if an inspector forgets to turn off the ignition timing fixing switch after the adjustment, the ignition timing is kept at the fixed value during the operation of the engine, even if engine operating conditions vary. Accordingly, malfunction of the engine such as miss fire occurs.
Japanese Patent Application Laid-Open 57-59059 discloses a system for resolving the above described problem. In the system, the ignition timing fixing switch which is kept on state is automatically turned off when a motor vehicle is driven. The motor vehicle driving condition is determined in accordance with parameters representing driving conditions such as output signals of an engine speed sensor, mass airflow meter, or intake manifold pressure sensor, vehicle speed sensor, throttle position sensor or position sensor for a select lever.
However, the sensors are liable to deteriorate with time. Accordingly, the system may fail to detect the driving condition when the sensors do not properly operate, resulting in fixing of ignition timing.